So, now that the “other thread” has gone on more than 1000 posts, I figured I would start another thread in an attempt to create a conversation about EFI tuning rather than instigating a never ending flame war. As such, this post/thread is in no way, shape or form intended to start a “tuner war”, nor is it intended to serve as an attack on any individual, or group, so let’s try to keep it clean.

I come from a bit of a bit of a diverse tuning background myself, but I won’t lie, this is my first German car. In the past I’ve owned a ’91 MR2 Turbo (I still miss that car), a 2nd Gen DSM, a Mazdaspeed 6, a 350Z, an Infiniti G37 and two turbo Subaru’s (’04 WRX & ’06 STI). During ownership of those vehicles, most of them were self tuned, on various devices/methods. I’ve been privileged enough to have been able to play with several different tuning tools (on other vehicles), although since I spent to much time in the Subaru community, much of my time behind a laptop was spent with either OpenECU or Cobb software. However, I’ve also played with a few different interfaces over the years on quite a few cars, like the old UTEC, DTEC, XEDE (Shiv’s old piggyback for Subaru’s/Mitsu’s back in the day), Apexi AFC, CP-E Standback (only on Mazda’s though, actually soldered the first one in the state of CO into a buddy of mine’s old MS3), ect, have even played with other ECU tuning software outside of Subaru’s (like DSMLink) and a couple standalone’s (AEM EMS & Hydra), however, with the standalones I did little other than just try to watch and learn the interfaces haha!!

With that said, I am not a professional tuner. I have a few good friends that tune for a living, but that has never been my intention, however it has been a longtime hobby of mine. As such, I figured I would share a few of the things I have learned over the years with this community. I don’t do this for a living; I’m just an enthusiast like most of you.

I think most of us on this board understand the basic concept behind the 4-stroke gasoline piston engine. While the N54/N55 are DI, they still fall under the basic concepts of a PI 4-stroke engine, which are fairly easy to understand. On the piston’s decent from the top of the cylinder, intake valves are opened allowing the cylinder to fill with air and fuel (PI engines spray towards the valve which is open, whereas DI engines are plumbed to spray directly into the cylinder). Granted, some DI setups are able to spray fuel well into the compression stroke (haven’t researched the N54/55’s fuel timing to say where during the process fuel is injected under full load), but that’s beside the point. After the cylinder is filled with air, it makes its ascent towards the top of the cylinder in what is referred to as the compression stroke. Towards the top of the compression stroke is where the spark plug fires, igniting the compressed air/fuel, which drives the piston back down (power stroke), and of course the piston’s next ascent pushes the burnt gases out of the exhaust valves (exhaust stroke).

This is a fairly simple concept. Although the main subject focus of what I’ll refer to as “never-ending debate thread” was timing and knock/detonation, which is what I’d like to focus on.

When people are referring to degrees of timing, they are referring to the number of degrees before the piston reaches top dead center that the spark plug fires (typically up to about 40 degrees). The reason the spark plug fires prior to the piston reaching TDC is that burning the air/fuel mixture takes time, and firing the spark earlier ensures that the burn is more complete, helping to force/push the piston downward during the power stroke. While low load (and subsequently temps due to lack of pressure/friction) typically requires more timing advance in order to get a more complete burn, under higher loads the air/fuel mixture burns faster, requiring less timing advance in order to complete a full burn in time to push the piston down during the power stroke.

Advancing ignition timing too much under higher loads can result in higher cylinder temperatures, causing detonation among other things. Very simply, detonation is just small uncontrolled explosions within your cylinder that are not part of the flame front (controlled flame created by sparking the air/fuel mixture with the plug). These small explosions, created by small pockets of air/fuel within the cylinder exploding due to excess heat/pressure, can range drastically in magnitude depending on conditions. They essentially create shock waves (which is why heavy detonation creates an audible pinging sound like shaking up BB’s in a can), the likes of which can do things like crack ringlands/piston rings, put holes in pistons ect. However, obviously due to the number of unbroken N54/N55’s out there, minor detonation can be fairly inconsequential in the short term. Although over the long-term, mild to moderate detonation can exasperate particle wear, which can cause various parts to wear prematurely as particles are carried throughout the oil system prior to being trapped in the oil filter.

The problem that many of the knowledgeable members of this community have with certain tuning devices (such as the JB3/4), is that they do not have anyway of modifying timing, which can be far from optimum when increasing load. To anyone who has tuned a somewhat modern EFI engine, the two tables you typically spend the most time adjusting are fuel tables (for cars with Open Loop mapping) and timing. These tables are fairly easy to understand, but I’m going to focus solely on timing tables. Here’s a timing table from a WRX for example:

^^^Reading this table is fairly simple. Your axes are RPM (y-axis) and engine load (x-axis). Engine load is typically calculated from one of two sensors on most cars, either the MAF/Mass Air Flow (no MAF on N54) or MAP/Manifold Absolute Pressure (aka speed density). A MAF is basically a hotwire that requires stays heated to a specific temperature via voltage, while a MAP sensor just senses total pressure. For this discussion, the load source doesn’t matter, all the matters is that both of them essentially measure air, which is what we use for a load site.

As you can see above, as you increase load at a certain RPM, timing advance is retarded. This principle is considered universal, as the higher the load, the faster the burn. You can also see as RPM increases, typically timing is advanced slowly. This is because the piston is increasing in speed, and as such needs more advance in order to complete a full burn at the end of the compression stroke. This is why under a constant load (doesn’t happen often on a turbo car as the compressor typically doesn’t hold full boost to redline), timing should be advanced slowly as piston speed increases (RPM’s increase).

The problem many knowledgeable members have with piggybacks that don’t modify timing is that they are modifying the load signal (MAP), in order to get the DME to increase boost pressure, without the DME being able to see the actual load site. This means the DME cannot adjust timing accordingly with the increased boost pressure. If you look at enough timing tables, you can see decreasing/retarding timing advance with load is a universally accepted rule. In essence, when doubling boost on these cars, actual load is increasing by close to ~25% (give or take), with no considerations for retarding timing. Honestly, if it wasn’t for the fact that it would likely result in fuel cut, CEL’s and loss of dynamic boost control, I would almost say that a cheap MBC would offer more consistency in this regard, as at least then the DME would be able to see the actual load on the motor and adjust timing accordingly based on the factory timing tables. However, I’m pretty sure BMW (like most manufacturers) implemented some sort of throttle plate induced fuel cut for overboost situations, and would likely throw a CEL to say the least.

I will say that from what I’ve learned in the short amount of time that I’ve been a part of this community is that these ECU’s (DME’s) seem to be much more reactive than they are proactive (compared to other vehicles), which I would say is the reason why we don’t see more blown motors IMO. The fact that fueling is closed loop full time (no preset load site based table) is evidence of this. These cars also seem to have highly sensitive knock sensors and are able to react quickly to these inputs. The direct injection cooling factor and placement of the injectors (close to TDC & the plug vs in the side of the head like some other DI cars) surely helps with making them more detonation resistant. Increasing load by ~25% without allowing the ECU to see the increase in load to adjust accordingly on other port injection turbo cars is a recipe for a blown motor in a short amount of time.

However, while less than optimal, the on-the-spot adaptability of these DME’s allows for blind increases in boost without any major consequences (at least not in the short term). While I do not advocate mindless flaming or instigation, at the same time I will agree with others in that relying on the knock sensor to set your base timing maps is far from optimal. When the DME senses light knock loads (it’s a good thing these aren’t rotaries, people would be replacing apex seals right and left haha!!), it pulls often drastic amounts of timing. While the speed and efficiency of the DME is impressive, saving motors from catastrophic failure, this does result in reduced consistency to say the least. Many dyno graphs with various dips are evidence of this. While using the factory boost level timing tables would be considered very aggressive, and on a clean run (preferably with higher octane fuel & cool ambient conditions) will produce impressive power numbers (comparable to competitors), at the same time, the result will not be as consistent as competitors who are more proactive with either allowing the DME to see full load (flash based tuning) or at least offsetting timing for the increased load (ala Procede via CPS offsetting ).

Obviously there is enough evidence to show that a basic JB3/JB4, on a “low-er boost map” is not going to cause a catastrophic failure, as the knock sensors are sensitive enough & the DME reacts fast enough to stave off major detonation. However, this is far from optimal IMO. Although I’m the type of person who believes in creating my own map, for my own car, at my elevation, running fuel I normally run in order to eliminate variables, and net optimum performance, consistency and safety out of my vehicle… but that’s a topic for another thread. Either way, I for one would concur that being more proactive (vs reactive) in regards to timing (and staving off detonation) would net increased consistency and potential long-term reliability.

Again, I am not attempting to bash anyone, or any tuning device on the market, but am simply sharing a bit of my own personal experience and thoughts on the matter. I’m not a professional tuner, just an enthusiast like most of you that’s been playing with turbocharged engines for a while now. I’m not a salesman, I have no grudges on this board, nor have I ever been sponsored by any tuning company associated with this platform. Anyone who would like to have a civil discussion about the matter, please feel free to share

Just my $.02

-Brandon

EDIT: For anyone who is interested, here is a stock timing table for the N54:

The problem that many of the knowledgeable members of this community have with certain tuning devices (such as the JB3/4), is that they do not have anyway of modifying timing, which can be far from optimum when increasing load.

This is just another disguised tuner bash. For whom may be interested, I have done some testing on a private road a few days ago with a friend's car which has a JB4 (he used Map 7). I have GIAC Stage 2.

The ignition timing was almost identical between my GIAC Stage 2 pump and his JB4 map 7. We compared the excel files in detail after the runs, we did graphs. Nevertheless he beat me but I have fewer mods I will ask for his permission to post some of the graphs.

Conclusion: the N54 ECU is not a Subaru ECU: it is more advanced. The knock sensors and knock ADAPTATION work very closely to ensure proper timing. At least from what I have seen, and I have seen hard data with back to back runs, not just talking and bashing.

No, this is clearly someone that has a basic understanding of engine tuning and is trying to enlighten the community.

Quote:

Originally Posted by tscdennab

The ignition timing was almost identical between my GIAC Stage 2 pump and his JB4 map 7. We compared the excel files in detail after the runs, we did graphs. Nevertheless he beat me but I have fewer mods I will ask for his permission to post some of the graphs..

You say you're running pump gas. Isn't map 7 on JB4 for race gas or meth? Your buddy should be able to run more timing than you. Why is he running almost identical timing?

Quote:

Originally Posted by tscdennab

Conclusion: the N54 ECU is not a Subaru ECU:

This is true

Quote:

Originally Posted by tscdennab

it is more advanced.

I'm not so sure. It certainly operates differently. The Subarus are tuned for maximum safe power, while the BMW is tuned to make consistent power. The N54 has a vast amount of headroom in the system. It can target a similar load at sea-level in sub-freezing weather as it can at 5,000 feet above sea-level on a 100* day.
The Subarus are actually known to have one of the most advanced knock control systems. You seem to have vast knowledge on the N54 knock control strategy. Please enlighten us all as to how it is better.

Quote:

Originally Posted by tscdennab

The knock sensors and knock ADAPTATION work very closely to ensure proper timing. At least from what I have seen, and I have seen hard data with back to back runs, not just talking and bashing.

What is your definition of proper timing? Does your definition include allowing the engine to knock?

You say you're running pump gas. Isn't map 7 on JB4 for race gas or meth? Your buddy should be able to run more timing than you. Why is he running almost identical timing?

Map 7 is a 16psi map. GIAC Stage 2 is a 16psi map. My buddy thinks it's ok to run without meth with IAT's of like 58F (14 Celsius). But he does run meth almost all the time, that night he ran without because we were doing some comparisons between the Wagner intercooler and the Helix (and they're almost identical as far as IATs). And from the timing logs, it seems that ECU drops the timing to identical values to GIAC, which really makes sense: the ECU thinks this is the correct timing to run in these conditions based on knock sensors (not based on boost, which it sees as stock boost) and adapts accordingly. From what I read from Cobb, the ECU is riding the knock sensors all the time, even with flashes, so that explains why the timing was identical for the same boost and same IATs.

The Subarus are tuned for maximum safe power, while the BMW is tuned to make consistent power.

In fact, it's the other way around. Subarus have predefined maps which means they make the same power even when the conditions vary (to a certain degree, of course). N54 is more dynamic and calculates many of the values "on the fly", whereas other ECUs have predefined values. That's why some days you feel the car a bit slow, some days you feel it is a beast.

Good post. Were the subarus you mention closed loop all of the time? Because if not, then you can't compare the two. I know the rx7s weren't, and you had to rely on user maps. These types of piggybacks would never have worked on an rx7. Just like the S-afc would not work-safely, that is. Maybe that's the reason for the confusion here?

It's also the reason you can't just slap on DPs an exhaust, and an intake and make 50hp with no tune. With an rx7 there was the 3 mod rule. Ever heard of that? Three airflow mods: intake, exhaust, downpipe. Any more than that and BOOM. Actually sometimes not, and sometimes even with less than three the engine went boom anyway. All it took was a hot day, or a bad tank of gas. Why? Because the ECU wasn't able to react. That's not the case here.

You're also incorrect in saying that the knock sensor is setting the BASE timing map. BMW sets the base ignition map and it does indeed look similar to the one you posted and does decrease timinq with load. I may be oversimplifying things here and somebody correct me If I'm wrong because I'm only repeating what I've read here, but it's my understanding that the flashes rely on the knock sensor as well, but with a 3 degree "head start".

i doubt you can run map 7 on JB4 on pump gas without seeing timing drops . Would be nice to see this logs.
I saw logs on jb4 running 15.5 psi on pump full stage 3 with 5C temps and there were timing dips in 4th and 5th .

Nice write up but most of this isn't relevant to the N54 which unlike your Subaru runs in an adaptive state at all times. If you add race gas to your car and it picks up timing then it's running off the knock threshold system. End of story. And I hate to break the news but all the tunes are including the stock tuning are.

This sort of sums it up from the other thread:

Quote:

Originally Posted by Mike@N54Tuning.com

By your definition then any tuning where the ignition advance increases when you add race fuel means tuning that is knocking. So the OEM tuning knocks, all the piggybacks knock, we'll soon see your Cobb tuning knocks as well. /thread.

Quote:

Originally Posted by clap135

That is absolutly correct. Glad you finally got it. Look up load vs timing tables, if the ecu is not hitting them, 99 percent chance you relied on the knock sensor to drop timing. And the cobb tune already knocks, look up ztuners or booms track logs.